An illumination device is known that illuminates a small and circular indicator such as the face of a watch, from an upper side of the periphery of the indicator. Such an illumination device can be exemplified by a front light (illuminator) including an annular light guide that emits light from the periphery of the face toward the center thereof, so as to illuminate the face.
FIG. 10 is a perspective view of a front light disclosed in Japanese Laid Open Patent Publication No. 2004-134223. As illustrated in FIG. 10, the front light 10 includes a light guide unit 9 having a light guide 12, and a light source unit 11. The light guide 12 includes an incident surface 12a, to which the light source unit 11 is attached. An emission surface 12b from which light led into the light guide 12 is emitted is provided along the inner circumference of the light guide 12. Along the outer circumference of the light guide 12, a reflecting surface 12c is provided. The reflecting surface 12c includes reflecting grooves 14 each having a wedge-shaped cross-section, so as to reflect the light toward the emission surface 12b. With the mentioned configuration, the front light 10 uniformly illuminates the circular region inside the light guide 12.
When it is desired to display various types of information in addition to simple indications of the time of day, an LCD panel is often employed in the face. As is widely known regarding information devices, the LCD panel looks nicer when lit by a backlight (planar light unit), rather than by a front light. On the other hand, an EL panel is often employed as backlight for an LCD panel of the face of a watch that is required to be designed in a small and thin shape.